Research in the fourth generation (4G) communication system, which is the next generation communication system, has been conducted to provide services of various Quality of Service (QoS) levels to users at a data rate ranging from about 100 Mbps to 16 Gbps. Particularly, the current 4G communication system is advancing to supporting high speed service with the guaranteed mobility and QoS in a broadband wireless access communication system, such as wireless local area network system and wireless metropolitan area network system.
Broadband wireless communication system developers are considering adopting a multi-hop relay data transfer scheme using a relay station for the sake of more efficient services in a wireless environment suffering severe change. The relay station can extend a coverage of a base station and enhance a throughput. In other words, when the relay station is positioned in a specific region in severe channel conditions, the throughput can be increased. Also, by installing the relay station near a cell boundary, a mobile station outside the coverage of the base station may receive service from the base station.
One of the techniques using a relay station is a collaborative Hybrid Automatic Repeat reQuest (HARQ), which is a kind of HARQ scheme using the relay station. In a collaborative HARQ scheme, when a packet error occurs at a receiving end, not only the transmitting end, but also the relay station, sends a retransmission packet to thus attain the diversity effect. Thus, the collaborative HARQ scheme can enhance the reliability of the retransmission packet.
However, the performance of the collaborative HARQ scheme may differ depending on the position of the relay station. When the retransmission is not taken into account and when the same Modulation and Coding Scheme (MCS) level is used, the application of the collaborative HARQ scheme may not achieve its full advantage. Further, even when a multiple antenna environment is virtually constituted with perfect independence, there is no method for utilizing the virtual multiple antenna environment because the transmitting end and the relay station retransmit the signal at the same time.